RESPIRATOKY SYSTEM. 



_ 



concerning the heat and purity of the blood in these creatures, , 

 prepared to find presenting the highest possible condition of 

 ment. Birds, in fact, breathe not only with their lungs, but the vital 

 element penetrates every part of the interior of their bodies, bathing 

 the surfaces of their viscera and entering the very cavities of their 

 bones ; so that the blood is most extensively subjected to its influence. 

 The lungs, in fact, are no longer closed bags as those of Keptiles are, 

 but rather resemble spongy masses, of extreme vascularity, firmly bound 

 down in contact with the dorsal aspect of the thorax, their posterior 

 surface being fixed to the ribs on each side of the vertebral column, and 

 entering deeply into the intercostal spaces. Such lungs are obviously 

 incapable of alternate dilatation and contraction; so that inspiration and 

 expiration must be provided for by a mechanism specially adapted to 

 the emergency. From an examination of fig. 360, the arrangement 



Fig. 360. 



B 



Inferior larynx and lungs of a bird. 



adopted will easily be understood. The bronchi derived from the bifur- 

 cated inferior extremity of the trachea plunge into the anterior face of 



